Analgesia after total hip replacement

We read with interest the article by Fischer and Simanski and would like to thank the authors for their review [1]. Peri-operative care for total hip replacement (THR) should take into account the need for excellent analgesia and early mobilisation. A variety of anaesthetic techniques is used for THR including central neuraxial blocks and general anaesthesia with a combination of major nerve or lumbar plexus block. A refresher on the nerve supply to the hip joint would enable anaesthetists to take a rational decision regarding nerve blocks for pain relief in the postoperative period. Sensory innervation to the hip joint is derived from the femoral, obturator, accessory obturator, sciatic, superior gluteal nerves and the nerve to quadratus femoris. The first three nerves are derived from the lumbar plexus and can be blocked at the lumbar plexus or at the femoral nerve level (the less reliable ‘3-in-1’ block). The superior gluteal nerve is formed from the dorsal divisions of L4, L5, S1 and the nerve to quadratus femoris from the ventral divisions of the L4, L5, S1 nerve roots. Both these nerves, along with the sciatic nerve, arise from the sacral plexus. The articular branches (to the hip joint) of the sciatic nerve are sometimes directly derived from the sacral plexus rather than from the sciatic nerve itself. The posterior cutaneous nerve of the thigh innervates the skin over the incision site for THR, which is also derived from the sacral plexus (dorsal divisions of S1, S2 and the ventral divisions of the S2, S3 nerve roots). A lumbar plexus block or a femoral ‘3-in-1’ block without a block of the sacral plexus does not provide consistent and reliable analgesia [2]. This is not surprising once one understands the nerve supply to the hip joint. In our view, if nerve blocks are chosen for postoperative analgesia, then they should block the nerves from lumbar and sacral plexus. The conventional posterior approach to block the sciatic nerve does not reliably block all the nerves from the sacral plexus that supply the hip joint. A combined lumbar and sacral plexus block has been described as a sole anaesthetic technique for hip operations [3]. Orthopaedic surgeons are keen to mobilise their patients as soon as possible, which may facilitate early discharge from the hospital. Major nerve blocks with or without catheters (especially sciatic nerve block) do not facilitate early mobilisation after THR and total knee replacement. If a single-shot femoral and sciatic nerve block is used, the duration of a numb and weak leg clearly depends on the strength of the local anaesthetic used. A concentrated solution provides prolonged analgesia but does not encourage early mobilisation, whereas a weak solution may not provide adequate duration of analgesia. In an attempt to find a balance between the anaesthetist’s and patient’s concerns for effective postoperative pain relief and the surgeon’s desire for early mobilisation we are conducting a trial of a modified continuous epidural infusion. Unlike a major nerve block, an epidural infusion can be turned on and off. Our theory is that if we stop the epidural at an appropriate time, the infusion-free period will allow the thicker motor and proprioception fibres to recover, while the thinner sensory fibers will remain blocked. This would allow the patient to mobilise and still be pain free. We infuse bupivacaine 0.125% in a range of 3–5 ml.h. The epidural infusion is stopped 2–3 h before the scheduled physiotherapy session (depending on the intensity of motor block). Once the physiotherapy is finished, the infusion is restarted (with or without a bolus) and the patient is kept pain free until the next day when the cycle is repeated. The epidural catheter is removed 48 h after the surgery and routine analgesia prescribed. We have put our theory to practice in a select, small number of cases. Though this is very labour intensive and needs close liaising with physiotherapists, ward nurses, the anaesthetic and the acute pain teams, our early observations are encouraging.